In the growth of the normal cells, cell division and its pause occur orderly according to the cell cycle, on the contrary, the growth of cancer cells is characterized by its disorderedness, thus the abnormality in the cell-cycle regulating system is presumed to be directly related to the oncogenesis and maligunant degeneration of cancer. The cell cycle of mammalian cells is controlled by a group of serine/threonine kinase called as cyclin dependent kinase (hereinafter denoted as “Cdk”) family. Cdk needs to form a complex with a regulatory subunit called cyclin, in order to exhibit its enzyme activity. Cyclins also have a family. Each Cdk molecule of which is considered to regulate progression at a specific stage of the cell cycle by forming a complex with the specific cyclin molecule which is expressed at the corresponding stage of the cell cycle. For example, D-type cyclin regulates the progression of G1 phase by binding to Cdk4 or Cdk6, and cyclin E-Cdk2 regulates the progression of G1/S boundary, cyclin A-Cdk2 regulates the progression of S stage, and furthermore, cyclin B-cdc2 regulates the progression of G2/M, respectively. In addition, there are three subtypes D1, D2 and D3 in D type cyclin. Furthermore, Cdk activity is considered to be regulated not only by the binding with cyclins, but also by phosphorylation/dephosphorylation of Cdk molecule, degradation of the cyclin molecule and binding with Cdk-inhibitor proteins. [Advances in Cancer Research (Advance Cancer Res.), Vol. 66, pp. 181-212(1995); Current Opinion in Cell Biology (Current Opin. Cell Biol.), Vol. 7, pp. 773-780 (1995); Nature (Nature), Vol. 374, pp. 131-134 (1995)].
The Cdk-inhibitor proteins of mammalian cells can be divided broadly into two categories, Cip/Kip family and INK4 family according to their structures and properties. The former inhibits a variety of cyclin-Cdk complexes broadly, whereas the latter inhibits Cdk4 and Cdk6 specifically [Nature (Nature), Vol. 366, pp. 704-707 (1993); Molecular and Cellular Biology (Mol. Cell. Biol.), Vol. 15, pp. 2627-2681 (1995); Genes and Development (Genes Dev.), Vol. 9, pp. 1149-1163 (1995)].
Cip/Kip family can be represented by p21 (Sdi1/Cip1/Waf1), and its expression induced by the tumor suppressor gene product p53 [Genes and Development (Genes Dev.), Vol. 9, pp. 935-944 (1995)]
On the other hand, p16 (INK4a/MTS1/CDK4I/CDKN2), for example, is one of the Cdk inhibitor proteins which belong to INK family. Human p16 gene is encoded on the chromosome 9p21. Abnormalities of this locus are detected with a high frequency in human cancer cells. Actually, a lot of cases of deletion and mutation of the p16 gene have been reported. Also, a high frequency of tumorigenesis in the p16 knockout mice has been reported [Nature Genetics (Nature Genet.), Vol. 8, pp. 27-32 (1994); Trends in Genetics (Trends Genet.), Vol. 11, pp. 136-140 (1995); Cell (Cell), Vol. 85, pp. 27-37 (1996)].
Each Cdk regulates the progression of cell cycle by phosphorylating the target protein at the specific phase of cell cycle, and retinoblastoma (RB) protein is considered to be one of the most important target proteins. RB protein is the key protein that regulates the progression from G1 phase to S phase. It is phosphorylated rapidly in the period from late G1 phase through early S phase. The phosphorylation is considered to be carried out by the cyclin D-Cdk4/Cdk6 complex, followed by the cyclin E-Cdk2 complex, leading the progression of cell cycle. The complex composed of hypophosphorylated RB and transcription factor E2F at dissociates when RB protein becomes hyperphosphorylated. As a result, E2F will become the transcriptional activator, and at the same time, the suppression of the promoter activity due to the RB-E2F complex will be removed, thus leading to the activation of the E2F-dependent transcription. At present, the Cdk-RB pathway, which consists of E2F and its suppressor RB protein, Cdk4/Cdk6 which repressively regulates the function of RB protein, Cdk inhibitor protein which controls the kinase activity of Cdk4/Cdk6, and D-type cyclin is thought to be the important mechanism to regulate the progression of G1 phase to S phase [Cell (Cell), Vol. 58, pp. 1097-1105 (1989); Cell (Cell), Vol. 65, 1053-1061 (1991); Oncogene (Oncogene), Vol. 7, pp. 1067-1074 (1992); Current Opinion in Cell Biology (Curren Opin. Cell Biol.), Vol. 8, pp. 805-814 (1996); Molecular and Cellular Biology (Mol. Cell. Biol.), Vol. 18, pp. 753-761 (1998)].
In fact, the DNA binding sequence of E2F is, for example, in the promoter region of many genes related to cell proliferation and are important during S phase. The transcription of more than one of them has been reported to be activated in an E2F-dependent manner during the period from late G1 phase to early S phase [The EMBO Journal (EMBO J.), Vol. 9, pp. 2179-2184 (1990); Molecular and Cellular Biology (Mol. Cell. Biol.), Vol. 13, pp. 1610-1618 (1993)].
Abnormalities of any factors composing Cdk-RB pathway such as deletion of functional p16, high expressions of cyclin D1 and Cdk4, and deletion of functional RB protein have been detected with a high frequency in human cancers [Science (Science), Vol. 254, pp. 1138-1146 (1991); Cancer Research (Cancer Res.), Vol. 53, pp. 5535-5541 (1993); Current Opinion in Cell Biology (Current Opin. Cell Biol.), Vol. 8, pp. 805-814 (1996)]. As all of them lead to abnormalities of promoting the progression from G1 to S phase, it is clear that this pathway plays a crucial role in tumorigenesis of cells or the neoplasia of cancer cells.
As for the known compounds having Cdk family inhibitory activity, a series of chromone derivatives represented by, for example, flavopiridol. (WO97/16447, 98/13344) are already known.
As the prior art structurally similar to the compounds of the present invention, there may be cited, for example, WO96/25157 (reference A), WO97/29743 (reference B), U.S. Pat. No. 5,696,138 (reference C) and Japanese Patent Publication for Laid-Open 115176/1989 (reference D).
References A and B disclose ureas or thioureas derivatives, both of which are substituted with the aryl groups on both N- and N′-positions. But, the aryl groups in the references A and B are completely different from nitrogen-containing heteroaromatic ring groups of the present invention in view of the chemical structure, thus it can be safely said that the compounds disclosed in the references A and B have no direct relationship with the compounds of the present invention. Furthermore, the use of the compounds disclosed in the references A and B is related to chemokine receptor antagonists, intended for producing a therapeutic agent for treating, for example, psoriasis, atopic dermatitis, asthma, chronic occlusive pulmonary disease and Alzheimer's disease, and so on, thus, having no relationship with the use of compounds of the present invention.
In the reference C, urea or thiourea derivatives are disclosed, having aromatic cyclic groups which may contain one nitrogen atom and benzene rings which may be condensed. The main compounds of the invention in the reference C are, however, urea derivatives substituted with two phenyl groups on the N- and N′-positions, and three urea derivatives substituted with a pyridyl group on the N′-position are disclosed only in the third column (on lines 11, 13 and 26), in the fifth column (on lines 17 and 19), in the seventh column (on lines 13 and 15), in the seventeenth column (on lines 24 and 42) and in the twentieth column (on the 14th line from the bottom of the column) of the specification. Descriptions in these columns are common. In addition, all the substituents, which exsist on the N-position of the urea compounds, are phenyl groups, thus the compounds are completely different from those of the present invention. Furthermore, in the case where the compounds of the reference C may have a fused benzene ring as the N-substituent, although it is defined that the ring structures which are fused with the benzene ring may be saturated or unsaturated, there is no description about the substituents on the fused ring, thus, said fused ring is interpreted to be non-substituted on the fused ring (in contrast, the compounds of the present invention have an oxo-group there). And, in addition, judging from the description in the reference C, the examples of the fused benzene ring are limited to naphthyl groups. Thus, the compounds in the reference C and those in the present invention differ in their chemical structures, and it can be said that the two inventions have no direct relationship with each other.
Furthermore, the use of the compounds described in the reference C is related to the potassium channel activators, as described in the sixteenth column, aiming at a therapeutic agent for treating, for example, potassium channel dependent convulsion, asthma, ischemia, and so on, so there is no relations of it with the use of the present invention.
In the Example 7 in the reference D, a urea compound wherein the N-position is substituted with a triazinyl group and the N′-position is substituted with a 9-fluorenone group.
The invention of the reference D is the one which relates to radiosensitive compositions, namely, photosensitive agents, and differs from the present invention in term of the technical fields they belong to, and also no other compound similar to the compound of the present invention is mentioned, except for that in the Example 7 described above. Because the compounds in the reference D are the compounds having various types of structure, that is, a triazine nucleus is used as the core structure, more than ten substituents containing a fluorenone group are applied at a photo-initiation part of the triazine nucleus, and more than ten combinations of connecting groups including urea, which connect a photo-initiation part and a triazine nucleus, are exemplified. Therefore, it is safely stated that the compounds of the present invention and the use thereof cannot be reached from the descriptions in the reference D including the compound in the Example 7, and the reference D is an invention which has no direct relation to the present invention.
Thus, since the present invention relates to the novel compounds which have not been described in the literatures yet and the novel use thereof, also the present invention can not be attained easily based on the above-mentnioned reference A to D.
Furthermore, up to date, no Cdk6 inhibitor is exemplified.
As stated above, some chromone derivatives can be exemplified as the compounds with Cdk family inhibitory activity, however, their inhibitory activity against Cdk4 is not strong enough, and compounds with a higher activity are still desired. More specifically, novel compounds which will simultaneously show heterogenous inhibitory activities, for example, against Cdk6 and so on, different from the known inhibitors, are desired.